The 50% effective intraperitoneal (ip) dose of Bothrops jararaca antivenom (ED50) was assessed in mice immediately (ED50 Oh) and thirty minutes (ED50 30') after the intramuscular (im) injection of two 50% lethal dose (LD50) of Bothrops jararaca venom. The efficacy of the antivenom injected at the venom inoculation site was assessed by the inoculation of two LD50 of the venom by im route, followed immediately (ED50 Oh) and 30 minutes later (ED50 30') by administration of the ED50 of the antivenom either entirely by the ip route or 50 percent ip plus 50 percent im, at the same inoculation site. It was shown that the ED50 30' was 3 times greater, than the ED50 Oh and that the antivenom was more protective to mice (lower death rate in 48 hours) when given entirely ip. It was concluded that, in this experimental model, a higher dose of bothropic antivenom is needed when the treatment is started lately, and that there is no benefit in its administration at the venom inoculation site.